With such an implement the impulsive blows imparted by the striker means necessarily involve high velocities of the piston and striker means in order to perform the required work. It is thus necessary to provide means to absorb the energy of the piston and striker means in the event of overtravel on the power stroke, for example when the tool breaks through the work or (when the implement is a portable hammer) the operator "lifts off" the implement from the work, to prevent shock damage to the casing and/or other parts. It has accordingly been proposed to provide an enlarged diameter portion for the piston and striker means which, on overtravel, enters a fluid-filled dashpot cavity to provide a snubbing action which damps the excessive overtravel of the piston means as the escape of fluid from the cavity as the enlarged portion enters the cavity is restricted. The invention has for its object to provide an implement with effective means for removing heat generated as a result of the damping action.